GB2387359A

GB2387359A - Control system for lift axles

Info

Publication number: GB2387359A
Application number: GB0207177A
Authority: GB
Inventors: Christopher Pickles
Original assignee: WHEELBASE ENGINEERING Ltd
Current assignee: WHEELBASE ENGINEERING Ltd
Priority date: 2002-03-27
Filing date: 2002-03-27
Publication date: 2003-10-15
Also published as: GB0207177D0

Abstract

A load carrying road vehicle has a main axle (3) and an adjustable supplementary axle (7) which are mounted beneath the vehicle chassis (1) via respective air springs (4, 8). There is also a pneumatic lifting device (9) for the adjustable axle (7). A Programmable Logic Controller (16) is connected to pressure and speed transducers (12, 13, 15) and also to solenoid control valves (10, 11) between the air springs (8) of the adjustable axle (7) and the lifting device (9). The adjustable axle (7) can be lifted and dropped e.g. in dependence on load carried by the vehicle or road speed. When it is dropped pressure is adjusted in the air springs (8) of the adjustable axle (7) to maintain a desired relationship with the pressure in the air springs (4) of the main axle (3).

Description

- - 1 ROAD VEHICLE AXLES

This invention relates to road vehicles having adjustable i.e. liftable or reloadable axles having suspension systems.

Load carrying road vehicles may have an adjustable supplementary 5 wheeled axle which can be moved between a stowed position at which it is lifted out of contact with the road surface, and an operational position at which it is dropped into engagement with the road surface to provide additional load support.

It is also known to provide an adjustable supplementary wheeled 10 axle which is 'reioadable' such that the loading, i.e. the percentage or ratio of weight taken by the axle, is alterable without necessarily lifting the axle off the road surface. By way of example, a road vehicle may have a drive axle and a reloadable supplementary axle with a 'dump facility' whereby the driver or operator by operation of a switch can 15 change the load carried by the supplementary axle from say 60% to 10% of the drive axle load. In this way a greater weight can be put on the drive axle to aid traction or reduce turning circle.

A lifted or unloaded axle may be adjusted, by dropping back into contact with the road surface or reloading, and this may be effected for 20 legal or safety reasons e.g. in correspondence with a predetermined change in certain conditions such as a predetermined increase in road speed or vehicle loading, or for operational reasons in accordance with driver or operator requirements.

- 2 The dropped or reloaded axle has suspension characteristics which desirably should accord with requirements and prevailing conditions.

An object of the present invention is to facilitate adoption of desired suspension characteristics for an adjustable axle when adjusted.

5 According to the invention therefore there is provided a load carrying road vehicle having one or more main wheeled axles mounted on the vehicle via one or more main suspension systems, and at least one supplementary wheeled axle mounted on the vehicle via a supplementary suspension system, the supplementary wheeled axle being adjustable by 10 movement between lifted and dropped positions and/or by unloading and loading thereof, characterized by the provision of- a control system operable on adjustment of the supplementary wheeled axle to effect automatic adaptation of the supplementary suspension system in dependence on control signals representing monitored vehicle parameters.

15 With this arrangement adoption of desired suspension characteristics for the adjustable axle when adjusted can be facilitated.

Adjustment of the supplementary wheeled axle may be achieved in any suitable manner. Thus, it may occur automatically, e.g. by automatic dropping of the lifted axle when road speed or vehicle loading exceeds a 20 predetermined value, and/or it may occur in response to driver or operator selection or demand e.g. by operation of a selector switch or the like.

With regard to the monitored vehicle parameters these may be of any suitable nature. In a particularly preferred embodiment the or one

- 3 such parameter relates to the main suspension system(s). Thus, for example, on dropping or reloading the supplementary wheeled axle the supplementary suspension system may be adapted to correspond on a predetermined basis to a suspension characteristic of the main suspension 5 system. The nature of the adaptation of the supplementary suspension system may also be of any suitable nature. Thus the adaptation may be of a simple on/off nature e.g. such that the adjustable axle is dropped or reloaded, and the supplementary suspension system then adopts a fixed 10 suspension characteristic in dependence on the monitored vehicle parameter. Preferably however, the nature of the adaptation is of a variable nature e.g. such as to modify the supplementary suspension system in correspondence with variation in the monitored vehicle parameter. 15 The supplementary suspension system may incorporate separate aspects, or even separate devices, associated respectively with the lifting and dropping or unloading and loading functions. Thus, the system may comprise a spring device, such as a pressurized air-spring device, for suspension purpose and a lifting device for lifting purposes. The axle 20 adjustment and the control system may be applied to either one of both of these.

In a particularly preferred embodiment the arrangement is such that the supplementary suspension system is automatically adapted to bear a

- 4 fixed proportional or other relationship with, e.g. to be substantially the same as, or 1:1 or 1:1.6 or other ratio to the main suspension system(s) with regard to a suspension characteristic such as resilience (weight at ground), resistance or travel. It is however also possible to maintain the 5 suspension characteristic of the supplementary suspension system substantially constant over a range of loads of the main suspension system. The main and supplementary suspension systems may be of any suitable kind but preferably comprise adjustable pressurised systems, 10 such as hydraulic or pneumatic systems. In the case of separate spring and lifting devices for the supplementary suspension system, the spring device may be a pressurized device such as an air spring and the lifting device may be a pressurised device or may be any other suitable kind of lifting device.

15 Where pressurised systems are used, fluid pressure may be monitored in all or part of the main system(s), and the control system may operate to effect automatic adjustment of fluid pressure in the supplementary suspension system e.g. to bring the pressures into line or into a predetermined or selected ratio.

20 Pressure control may be effected with one or more solenoid valves which may be operable to open and close to increase and/or decrease and/or maintain fluid pressure e.g. by venting fluid or admitting fluid from a pressurised source, and which may be 3-stage valves. Operation of the

- 5 valves may occur on any suitable basis e.g. in a single operational step, continuously, or in multiple steps.

The control system may include a Programmable Logic Controller or other computerized device. This device may perform continuous or 5 multiple monitoring and/or control steps e.g. by repeated monitoring and adjustment to attain the desired suspension characteristics of the adjustable axle.

Provision may be made for intervention with, e.g. by overriding, some or all of the actions of the control system and manual or electrical 10 controls may be provided for this purpose.

The vehicle may be of any suitable kind and thus may be any form of multiaxle on or off road commercial vehicle or trailer, a load transport road trailer, or a lorry, or the like.

If desired, the control system may also be utilised for other functions e.g. to adjust a braking circuit associated with one or more of the axles so that for example when the adjustable axle is lifted or unloaded the braking force can also be correspondingly adjusted.

The invention is not restricted to adaptation of the supplementary suspension system following dropping or reloading of the adjustable axle.

20 It may also apply to adaptation following unloading or in relation to other adjustments. The invention will now be described further by way of example only and with reference to the accompanying drawings in which:

- 6 Figure 1 is a diagrammatic side view of a road vehicle traction unit in accordance with one aspect of the invention; and Figure 2 is a diagram of a control system of the unit.

Referring to the drawings, Figure 1 shows a road vehicle traction 5 unit comprising a rigid chassis 1 made from interconnected steel beams.

A wheeled load supporting trailer (not shown) having a platform or container is in use connected to the chassis to be driven thereby.

The chassis 1 has at its front end a cab 2 with road wheels and engine. 10 The chassis 1 has a pair of closely spaced wheeled axles 3, 7 which are mounted beneath the chassis 1 via respective pneumatic suspension components (air springs) 4, 8.

These air springs 4, 8 are connected via air lines 5 to a source of pressurized air 6 which may be fed by a compressor driven by the traction 1 5 unit engine.

The axle 7, which is inwards of the rearmost axle 3, is an adjustable supplementary wheeled axle 7. The rearmost axle 3 is a driven axle. This supplementary axle 7 is mounted beneath the chassis 1 via its 20 respective supplementary pneumatic suspension components (air springs? 8.

Also, a powered lifting device 9 is provided which in this case, as shown in Finure 2 comprises a pneumatic lift device.

- 7 Three stage solenoid valves 10, 11 are interposed between the air springs 8 and the lift device 9 and the source 6 of compressed air.

Pressure transducers 12, 13 are connected to the main air supply line 5 for the air springs 4 and the air springs 8. These transducers 12, 5 13 produce electrical signals representative of monitored air pressure.

There is also a speed transducer 15 which monitors vehicle road speed and produces an analog electrical signal representative of the - speed. The solenoids 10, 11 and the pressure and speed transducers 12, 10 13, 15 are connected to a microprocessor-based control device 16 which incorporates in this case a Programmable Logic Controller. This device 16 may be mounted on the chassis 1 or in the traction unit cab. The device 16 is connected to the vehicle electrical system and also is connected to control switches 17, 18 in the cab, including lift and drop switches.

15 In use, by operating the lift and drop switches 17, 18, control signals are fed to the solenoid 11 to cause pressurised air to be admitted to or vented from the lift device 9 correspondingly causing the axle 7 to be pneumatically lifted to a stowed position where the axle wheels are out of contact with the road surface and an operational position at which 20 the axle 7 is free to drop downwardly bringing the wheels into contact with the road surface.

When the axle 7 is dropped signals are fed to the other solenoid 10 to pressurise the air springs 8 as necessary and thereby hold the wheels

- 8 of the supplementary axle 7 in load-supporting engagement with the road surface. As an alternative to operation of the drop switch 18, the supplementary axle 7 may also drop automatically, in the manner 5 described above, when the monitored pressure in the main air springs 4 indicates that the load carried by the vehicle exceeds a predetermined value in relation to other monitored parameters such as road speed.

When the axle 7 is in the dropped position, the pressure in the springs 8 monitored with the transducer 13 is compared with the pressure 10 of the main air springs 4 monitored with the transducer 12 and signals are fed to the solenoid 10 to open or close the solenoid valve thereby to increase pressure in the supplementary axle air springs 8, or reduce such pressure by venting or maintain existing pressure, with the objective of maintaining the pressures in the air springs 4, 8 the same or of a desired 15 relationship within an acceptable range.

This monitoring and/or pressure adjustment may be effected on a continuous or periodic basis.

By way of example, in the case where the driven axle 3 has a spring pressure of 6.0 bar as indicated by sensor signals, and the desired 20 spring pressure of the supplementary axle 7 is 4.0 bar, the control system operates automatically to adjust the spring pressure of the axle 7 to achieve the required 1.5: 1 ratio.

Thus, if the pressure is 4.3 bar the control system causes the

- 9 - solenoids to vent air from the circuit. This occurs repeatedly in small steps until the correct balance is achieved.

If the pressure is 3.7 bar the control system causes the solenoids to allow a small amount of pressurised air from the source (air tank) to 5 flow to the circuit to increase the pressure. This occurs repeatedly in small steps until the correct balance is achieved.

When the pressure is 4.0 bar within a pre-programmed tolerance range (say +0.1 to -0.1 bar) the control system causes the solenoids to remain closed.

10 With this arrangement it can be assured that the supplementary axle 7 is always maintained in optimum operational conditions, particularly with regard to safety considerations. The described arrangement also permits ready adaption of the supplementary suspension system to meet operating conditions, which may involve increased or decreased 15 suspension pressure, as selected by the driver or operator.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

Claims

- 10 CLAIMS

1. A load carrying road vehicle having one or more main wheeled axles mounted on the vehicle via one or more main suspension systems, and at least one supplementary wheeled axle mounted on 5 the vehicle via a supplementary suspension system, the supplementary wheeled axle being adjustable by movement between lifted and dropped positions and/or by unloading and loading thereof, characterized by the provision of a control system operable on adjustment of the supplementary wheeled axle to 10 effect automatic adaptation of the supplementary suspension system in dependence on control signals representing monitored vehicle parameters.

2. A vehicle according to claim 1 characterized in that adjustment of the supplementary wheeled axle is automatic.

15 3. A vehicle according to claim 2 characterized in that the automatic adjustment consists of dropping of the lifted said axle when road speed exceeds a predetermined value.

4. A vehicle according to claim 2 characterized in that the automatic adjustment consists of dropping of the lifted said axle when vehicle 20 loading exceeds a predetermined value.

5. A vehicle according to claim 1 characterized in that adjustment of the supplementary wheeled axle occurs in response to driver or operator selection.

- 11 6. A vehicle according to any one of claims 1 to 5 characterised in that the (or one) said monitored vehicle parameter relates to the said one or more main suspension systems.

7. A vehicle according to any one of claims 1 to 6 characterised in 5 that the said adaptation is of a variable nature.

8. A vehicle according to claim 7 characterised in that the supplementary suspension system has a fixed proportional relationship to the said one or more main suspension systems with regard to a suspension characteristic.

10 9. A vehicle according to any one of claims 1 to 7 characterised in that the supplementary suspension system incorporates separate devices associated respectively with the lifting and dropping or unloading and loading functions.

10. A vehicle according to claim 8 characterised in that the separate 15 devices comprise a spring device for suspension purposes and a lifting device for lifting purposes.

11. A vehicle according to any one of claims 1 to 10 characterised in that the supplementary and main suspension systems are pressurised fluid systems and the control system is operable to 20 effect automatic adjustment of fluid pressure in the supplementary suspension system.

12. A vehicle according to claim 11 characterised in that pressure control is effected with one or more solenoid valves.

- 12 13. A vehicle according to any one of claims 1 to 12 characterized in that the control system includes a computerized device which effects repeat monitoring and adjustment of suspension characteristics of the supplementary wheeled axle.

5 14. A vehicle according to claim 13 characterized in that the computerized device is a Programmable Logic Controller.

15. A vehicle according to claim 1 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. :